The trail that led to the doorstep of Osama bin Laden in Pakistan began years earlier with aggressive interrogations of al-Qaida detainees at the U.S. detention facility at Guantanamo Bay and CIA “black site" prisons overseas, according to U.S. officials.

It was those sometimes controversial interrogations that first produced descriptions of members of bin Laden’s courier network, including one critical Middle Eastern courier who along with his brother was protecting bin Laden at his heavily fortified compound in Abbottabad on Sunday. Both the courier and his brother were among those killed, along with bin Laden, in the dramatic raid by U.S. special forces.

The behind-the-scenes story of how bin Laden was finally located is yet to be fully told, but emerging details seem likely to reignite the debate over whether “enhanced interrogation” techniques and other aggressive methods that have been widely criticized by human rights groups provided useful – or timely -- intelligence about al-Qaida. While some current and former U.S. officials credited those interrogations Monday with producing the big break in the case, others countered that they failed to produce what turned out to be the most crucial piece of intelligence of all: the identity and whereabouts of the most important figure in bin Laden courier's network.

“Multiple sources of intelligence led us to where we are,” one senior U.S. intelligence official, who like the others spoke on condition of anonymity, told reporters on Monday. “Key information was gleaned from detainees (and) that detainee reporting provided insight into the (bin Laden) courier network.”

'20th hijacker' may have fingered courier
The identity of at least one of the detainees who provided early information about the courier who led to bin Laden could be politically explosive. According to a U.S. official, that detainee was notorious Saudi al-Qaida operative and accused 9/11 conspirator Mohammed al-Qahtani, who was subjected to some of the most humiliating interrogations at Guantanamo. Among the enhanced interrogation techniques used on him were being forced to wear a woman’s bra, being led around on a leash and forced to perform dog tricks and being subjected to cold temperatures that twice required his hospitalization, according to a later U.S. military report.

U.S. officials have accused Qahtani of being the so-called 20th hijacker for the 9/11 plot based on his unsuccessful attempt to enter the U.S. in August 2011 at the Orlando airport, where lead hijacker Mohammed Atta had arrived to meet him.

But in January 2009, Susan Crawford, then chief of the U.S. military commissions under President George W. Bush, rejected the proposed prosecution of Qahtani because of what had been done to him in interrogations at Guantanamo. “His treatment met the legal definition of torture,” Crawford told the Washington Post’s Bob Woodward.

It is unclear what Qahtani, who was captured in January 2002, told interrogators about the crucial bin Laden courier and whether he was fully honest. While Liz Cheney and other conservatives on Monday tried to portray the bin Laden raid as vindication of the intelligence community’s tough interrogations of “high-value” detainees, other details suggest that the most aggressive “enhanced interrogation” techniques -- including waterboarding, against other detainees, particularly 9/11 mastermind Khaled Sheikh Mohammed -- proved useless in learning the identity of the bin Laden courier.

As first described by U.S. officials in a background briefing early Monday morning, U.S. intelligence officials spent years trying to piece together information about bin Laden’s courier network, hoping that they could lead them to the elusive al-Qaida leader.

“One courier in particular had our constant attention,” one senior U.S. official said. “We identified him as a protégé of Khaled Sheikh Mohammed and a trusted assistant to Abu Faraj al Libi,” who succeeded Mohammed as al-Qaida’s No. 3 after Mohammed’s capture.

Humiliating interrogations
After Qahtani was subjected to some of the humiliating interrogations at Guantanamo that later became public, he started to cooperate and, for a while, provided a wealth of information about al-Qaida, including references to the courier in question, the U.S. official said. An October 2008 Defense Department document about Qahtani, identifying him as Maad al Qahtani, recently released by WikiLeaks, detailed a long history of involvement with al-Qaida, including spending time at training camps and guest houses in Afghanistan and fleeing with bin Laden through the caves of Tora Bora in November 2001. (Qahtani later clammed up, repudiated what he had previously said and stopped cooperating.)

In addition, a senior U.S. intelligence official told NBC News investigative producer Robert Windrem that both Mohammed, who was repeatedly waterboarded by the CIA, and al Libi, who was aggressively interrogated but not waterboarded, provided the nom de guerre of the courier. Mohammed was among the “high-value detainees” subjected to specially approved “enhanced” interrogations at secret sites overseas, including CIA-run prisons in Poland, Romania, Thailand and elsewhere, according to U.S. officials.

But U.S. officials stressed that none of the detainees at that point offered up the real identity of the courier. “All we had was the nom de guerre,” said the U.S. official. To one counterterrorism expert who has sharply criticized the CIA’s interrogations, the failure of any of the high-value detainees to provide the identity of the courier raises fresh questions about the value of the information the agency was receiving from enhanced interrogations.

“They waterboarded KSM (Khaled Sheikh Mohammed) 183 times and he still didn’t give the guy up,” said one former U.S. counterterrorism official who asked not to be identified. “Come on. And you want to tell me that enhanced interrogation techniques worked?"

It is possible that neither Qahtani nor Mohammed knew the true identify of bin Laden’s trusted courier, although that would appear to contradict the U.S. official’s description of him as Mohammed’s “protégé.”

In the end, U.S. officials say, it took years of patient intelligence work -- including information gleaned from multiple detainees and other sources of intelligence -- to enable the CIA to figure out who the courier was.

“Four years ago, we uncovered his identify,” said a senior U.S. official. Two years later, the U.S. officials were able to trace the courier and his brother to the area in Pakistan where they finally found bin Laden.

Video: Mission accomplished: The end of bin Laden

Closed captioning of: Mission accomplished: The end of bin Laden

>>>laden is dead. the man who killed thousands of innocent people. the man who launched the
united states
into two wars in the name of that attack, the man who changed the way we have to live in this country. the man who did all of this was killed by
u.s. special forces
acting on orders from
president obama
. we first learned his name back when there was still smoke rising from
ground zero
behind us here. the u.s. came close to getting him, but could not. he was villainized. he became something of a cartoonish cave-dwelling creature
over time
. in the end, though, we learned he was living well, under
deep cover
, but it wasn't deep enough. as the presidential and his
national security
team watched on
live tv
in the
white house
, two choppers full of americans landed on his compound in pakistan, rappelled down ropes and began attacking. he's already been buried at sea. a chapter is over while a new one begins. we have comprehensive coverage for you.
jim
remains on duty at the pentagon to start us off.

>> reporter: the cia made it official today that
dna testing
positively confirmed the navy s.e.a.l.s gauot their man. the massive compound that was
osama bin laden
's base of operations sat empty today after u.s. operations pulled off their daring nighttime raid. it was
president obama
who broke the news.

>>tonight, i can report to the
american people
and the world that the
united states
has conducted an operation that kill killed
osama bin laden
, the leader of
al qaeda
.

>> reporter: it was half
past midnight
in pakistan. american helicopters loaded with navy s.e.a.l.s hugged the ground to avoid detection from pakistani radar as they closed in for the kill. as they reached the compound,
small arms
fire erupted from the rooftops and then panic. one of the helicopters lost altitude and was forced to land in the middle of the compound. no americans were injured, and in minutes, a dozen commandos were looking for
osama bin laden
. in a firefight that lasts 40 minutes, the s.e.a.l.s killed two operatives on a small building on the edge of the compound. they then cysystematically went room by room where they found
osama bin laden
and his son. as the s.e.a.l.s closed in,
bin laden
opened fire. the s.e.a.l.s fired back, killing
bin laden
and a woman.
bin laden
was the last to die with at least one gunshot to the head. this video obtained by abc reportedly showed the room where been laudb win laden. they believe there was no other way out.

>>the word was
osama bin laden
would not surrender, and his
security agents
had been told to kill him if it looked like they were going to lose him to a u.s. snatch operation.

>> reporter: the commandos departed with
bin laden
's body, and before the
end of the day
, his body was aboard the u.s.s.
carl vinson
where he was given a proper muslim burial at sea. u.s. officials tracked him down, while the
u.s. military
took him out.

>>this is what we call a clean hit and a solid piece of work from an intelligence and special opralgzs standpoint.

>> reporter: and that windfall may just be beginning. navy s.e.a.l.s recovered large volumes of
computer data
and hard drives. so much of it that could provide valuable intelligence on
al qaeda
. there's so much of it that they have created an entire
task force
all its own just to wade through it.

>>jim
, after a long night on the story and a long day at the pentagon,
jim
, thanks.

Timeline: A timeline of Osama bin Laden's life

Considered enemy No. 1 by the U.S., the Saudi millionaire is the perpetrator behind the Sept. 11, 2001, attacks. Click on key dates to learn more about the founder of al-Qaida, an international terror network.

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